Sains Malaysiana 48(2)(2019): 435–442

http://dx.doi.org/10.17576/jsm-2019-4802-22

Aggregation and Stability of Iron Oxide and Alumina Nanoparticles: Influences of pH and Humic Acid Concentration

(Pengagregatan dan Kestabilan Oksida Besi dan Zarah Nano Alumina: Pengaruh pH dan Kepekatan Asid Humik)

NUR SURAYA AHMAD^1*, SHAHIDAN RADIMAN¹ & WAN ZUHAIRI WAN YAACOB²

¹School of Applied Physics, Faculty of Science and Technology, 43600 UKM Bangi, Selangor Darul Ehsan, Malaysia

²School of Environmental and Natural Sources Sciences, Faculty of Science and Technology, 43600 UKM Bangi, Selangor Darul Ehsan, Malaysia

Diserahkan: 2 Mei 2018/Diterima: 19 Oktober 2018

ABSTRACT

The scenario of released nanoparticles from consumer products into the environment especially natural waters has become a great concern nowadays. Assessing their aggregation and stability under environmental conditions is important in determining their fate and behavior in natural waters. The aggregation behavior of selected nanoparticles (iron oxide and alumina) was investigated at variable concentrations of humic acid (5, 10, 50 mg/L), and pH variation in solution. Dynamic light scattering was used to measure their z-average hydrodynamic diameter and zeta potential. Derjaguin-Landau-Verwey-Overbeak (DLVO) theory was used to explain the thermodynamic interactions between two particles. Then, the stability was evaluated by assessing their aggregation. The increasing of humic acid concentrations enhanced aggregation of iron oxide and alumina nanoparticles, particularly at low pH levels. The maximum aggregation was found in pH below the point of zero charge (PZC) due to electrostatic destabilization and electrostatic stabilization that took place at pH above the point of zero charge. Meanwhile, at pH point of zero charge, nanoparticles were coated with negative humic acid charged. From this study, properties of nanoparticles (size, surface charge, Hamaker constant) and environmental condition (humic acid concentration, pH) have their specific roles to control the fate and behavior of nanoparticles in environmental media.

Keywords: Aggregation; DLVO; nanoparticles; stability

ABSTRAK

Pada masa ini, peningkatan senario pelepasan zarah nano daripada produk pengguna ke persekitaran terutamanya ke dalam air semula jadi amatlah membimbangkan. Penilaian agregasi dan kestabilan zarah nano adalah penting untuk menentukan keadaan dan tingkah lakunya di dalam kandungan air semula jadi. Kajian mengenai tingkah laku agregasi zarah nano (oksida besi dan alumina) pada pelbagai kepekatan asid humik (5,10,50 mg/L) dan pH yang berlainan dijalankan. Penyerakan cahaya dinamik digunakan untuk mengukur purata diameter hidrodinamik dan nilai keupayaan zeta. Teori Derjaguin-Landau-Verwey-Overbeak (DLVO) digunakan untuk menerangkan tindak balas termodinamik antara dua zarah. Kemudian, kestabilan dinilai berdasarkan tingkah laku agregasi. Peningkatan kepekatan asid humik telah menggalakkan/meningkatkan tingkah laku agregasi zarah nano oksida besi dan alumina pada pH yang rendah. Agregasi maksimum dijumpai pada pH di bawah caj titik sifar yang disebabkan oleh ketidakstabilan elektrostatik dan kestabilan elektrostatik dilihat berlaku pada pH di atas pH caj titik sifar. Manakala, pada caj titik sifar, zarah nano disaluti dengan caj asid humik yang bersifat negatif. Keputusan daripada kajian ini mendapati sifat zarah nano (saiz, caj permukaan, pemalar Hamaker) dan keadaan persekitaran (kepekatan asid humik dan pH) memainkan peranan yang penting dalam mengawal keadaan dan tingkah laku zarah nano pada medium sekitaran.

Kata kunci: Agregasi; DLVO; kestabilan; zarah nano

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*Pengarang untuk surat-menyurat; email: nursuraya_ahmad@siswa.ukm.edu.my